Thousands of Hong Kong students will begin a week-long boycott of classes Monday, the start of what democracy activists say will be a wider campaign of civil disobedience against Beijing's refusal to grant the city full universal suffrage.

China dashed hopes last month for full and unfettered democracy in the former British colony when it announced plans to vet nominees who want to stand as its next leader.

A coalition of pro-democracy groups, led by Occupy Central, have labelled Beijing's restrictions a "fake democracy" and have vowed a series of actions including a blockade of the city's financial district.

Laying the groundwork for what activists call "a new era of civil disobedience", thousands of students from more than 25 universities and colleges will take part in the week-long strike from Monday to voice their anger.

The strike could breathe new life into the democracy campaign, which recently lost some steam after its senior leaders conceded that Beijing was highly unlikely to change its mind whatever they do.

"This is a turning point," Alex Chow, chairman of the Hong Kong Federation of Students, told AFP. "The government has to respond to what so many Hong Kong people are calling an unfair election system."

The student agitation comes a week after more than 1,500 activists marched through Hong Kong's streets carrying huge sheets of black cloth and banners demanding genuine universal suffrage.

That marked the first sizeable protest since China's National People's Congress (NPC) ruled in late August that candidates for the 2017 polls will be vetted by a pro-Beijing committee -- and just two or three approved nominees will be allowed to stand.

The city's democracy activists are demanding free and open nominations for the chief executive, the top government post.

The success of the university strike -- an echo of the student-led Tiananmen movement in Beijing that was brutally crushed 25 years ago -- will be determined by the scale of the turnout, Chow said.

- 'Battle for public opinion' -

The students can point to their success in 2012, when they were at the forefront of protests against plans by the Hong Kong government to institute a "national education" curriculum seen as pro-China. The government eventually backed down.

But in Beijing, the rhetoric in official media has remained unrelenting against any concessions to the Hong Kong democracy movement, which some in the Communist regime see as an insidious threat to their rule of the country as a whole.

More than 3,000 students from Hong Kong's two main prestigious universities alone are expected to join the strike, organisers predict.

"The legitimacy of the Hong Kong government is very, very low at this stage, and in this situation we wish to redefine the direction of Hong Kong," said Yvonne Leung, president of the Hong Kong University student union, urging the NPC to reverse its ruling.

The strike marks the beginning of the "battle for public opinion" in Hong Kong, said Sonny Lo, a professor at the Hong Kong Institute of Education.

"The class boycott is... a testimony to the students' affinity to the Hong Kong political and legal identity," Lo added.

The NPC's verdict still needs to win two-thirds support in Hong Kong's 70-seat legislature, where pro-democracy lawmakers control slightly over a third of seats. All 27 pan-democrats have pledged to reject the vetting plan.

Britain handed Hong Kong back to China in 1997 under a "one country, two systems" agreement which allows civil liberties not seen on the mainland, including free speech and the right to protest.

Public discontent has been growing over rising inequality, increased political interference and the perceived cosy relationship between the city's powerful business elite and Beijing.

However, opinion polls suggest only lukewarm support for direct action such as the mass sit-in of the Central district promised by the Occupy movement, which will be watching the student strike closely as it plots its next move.